Plankton make useful indicators for large scale environmental change in our oceans. Firstly, they are very sensitive and responsive to changes in their environment, so changes in plankton ‘reflect’ wider climatic and oceanographic processes. Secondly, as the base of the marine food web, changes in plankton communities can themselves ‘affect’ organisms at higher trophic levels such as fish and seabirds. Incorporating climate-driven changes in plankton into the policy process however, is not clear. As a policy focusing on direct anthropogenic pressures that are manageable at the regional scale, the European Marine Strategy Framework Directive, for example, regards these wider environmental influences as “prevailing conditions”. To this end, if a change in plankton communities linked to climate is detected during assessments, these changes don’t contribute to plankton communities missing their target of ‘Good Environmental Status’. These definitions of GES targets and ‘prevailing conditions’ ensure targets are realistic and achievable, and management measures are implemented efficiently. The question then arises however, if we find a change in plankton communities linked to prevailing conditions during an ecosystem assessment, how can we best use this information?

This is where the concept of ‘surveillance indicators’ comes in, first outlined in a paper by Shephard et al. (2015) They classify this new type of indicator as those that don’t have clear, quantifiable relationships with direct pressures, but can still inform on wider influences of human activities or underlying environmental change. Clearly, this type of information is important. We know through long term studies that marine ecosystems vary as a result of environmental variation, and are changing as a result of anthropogenic climate change. A strong understanding of these underlying changes in prevailing environmental conditions is needed to effectively assess and manage marine biodiversity under the MSFD.

In our new paper published in Marine Policy, we illustrate that plankton can play a key ‘surveillance role’ in marine ecosystem assessments, by informing on changing ‘prevailing conditions’. Specifically, we outline a ‘diagnostic role’ of this plankton surveillance information which aids in understanding the relative influence of prevailing conditions over direct pressures on the ecosystem, and a more ‘strategic’ role, which aids in setting adaptive targets and management measures to climate change. Importantly, this surveillance role would be additional to the primary role of plankton indicators in assessing for Good Environmental Status against more direct pressures such as eutrophication. Ultimately, plankton indicators can have a key role for the management and conservation of our marine environment, even if during an assessment indicator changes are not found to be driven by a directly manageable anthropogenic pressure.